Selenium RC was the main Selenium project for a long time, before the WebDriver/Selenium merge brought up Selenium 2, the newest and more powerful tool.

Now Selenium 1 is deprecated and is not actively supported (mostly in maintenance mode).

Selenium 2.0

Selenium 2 is the future direction of the project and the newest addition to the Selenium toolkit, which provides all sorts of awesome features, including a more cohesive and object oriented API as well as an answer to the limitations of the RC.

Both Selenium and WebDriver developers agreed that both tools have advantages and that merging the two projects would make a much more robust automation tool. Selenium 2.0 is the product of that effort.

It supports the WebDriver API and underlying technology, along with the Selenium 1 technology underneath the WebDriver API for maximum flexibility in porting your tests.